The Devils Marbles final

The Rock Cycle and Erosion The rock cycle is a dynamic process that explains the transitions between igneous, sedimentary and metamorphic rocks (The Rock Cycle, 2014).It is the basic concept that describes the formation, breakdown and reformation of rock (The Rock Cycle, n.d.). The original concept was developed by James Hutton (1726-1797) and later Charles Lyell (Rock Cycle, 2014). The main idea is that every rock is continually changing from one type to another. This occurs as the rock is exposed to weathering and erosion before undergoing compaction and cementation. The newly formed rock then sinks, becoming subject to extreme heat and pressure (Figure 2) (The Rock Cycle Diagram, n.d). Intrusive igneous rock is formed when magma within the earth cools and solidifies. This process is known as crystallisation (Whalley et al, 2004, p.256). As a consequence of the slow cooling process, intrusive igneous rocks have large interlocking crystals (Gould et al, n.d). Extrusive Igneous rocks are formed when magma reaches the surface and the lava above the Earth cools. This process is a lot faster than when igneous rocks are formed underground and consequentially have considerably smaller crystals (Whalley et al, 2004, p.256). Sedimentary rock is formed from sediment which is composed of a combination of rock fragments and decomposed fossils (Whalley et al, 2004, p.257). Sediment is formed when rocks above or near the surface are altered and broken down by direct effects of the atmospheric conditions (Hallam, 1977, p.46). This process which can occur either by physical, chemical, or, biological weathering (Earth, 2009, p 110). These fragments are then transported by eroding agents such as wind, rain and ice. (Overview of Geological Fundamentals, 2014). The sediment then builds up layers of deposited rocks. The pressure and weight of the material above then compacts the sediment and reduces air gaps. (Overview of Geological Fundamentals, 2014) Cementation then occurs which is when water seeps through the rock cementing the particles together (Whalley et al, 2004, p.257). The formation of metamorphic rocks occurs when sedimentary or igneous rocks are changed due to extreme heat and pressure (Rock Cycle, 2014). Many rock formations show evidence of the occurrence of weathering and erosion. The Twelve Apostles are an example of how weathering and erosion can affect landforms. The cliffs are under constant attack from sea, rain, sea- spray, water and wind which carries abrasive sand and gravel (Lech and Trewin, 2013). Firstly, the limestone cliffs are undercut by waves and the formation of caves occur. Then the caves widen creating arches, and as time progresses the arches collapse leaving the stacks. These stacks then erode, primarily by waves but also by other eroding agents causing the stacks to collapse (Lech and Trewin, 2013). The Twelve Apostles are evidence supporting the occurrence of erosion and the different stages of this process are visible (Figure 3). Wave rock is another example supporting the occurrence of weathering and erosion. Its shape is a result of wind and water erosion which has undercut the base leaving behind the rounded overhang (Wave Rock, 2014).The effects of weathering and erosion are visible on Wave Rock by the vertical streaks of various colours. These streaks are present due to runoff water running down the rock and dissolving and re-depositing minerals in the rock (Figure 4)(Monroe,2011). The Bungle Bungles have been formed by sedimentation, compaction, uplift and erosion (UNESCO World Heritage Centre, 1992-2014). The sandstone that the beehives are made of formed when rivers deposited layers of sediment in a shallow depression (Lech and Trewin, 2013). Compaction and sedimentation nt then occurred as described in the rock cycle (Overview o f Geological Fundamentals, 2014). The beehives were shaped by physical weathering which is the process where rocks are broken into fragments without much change to their chemical composition and also by erosion by wind, rain, running water and plants and animals (Figure 5) (Lech and Trewin, 2013). Figure 2. Diagram of the rock cycle (The rock cycle,n.d.) Figure 3. The Twelve Apostles (Will Cox, 2012) Figure 3. Wave Rock (Vicki Fraser, 2011) Fi ure 5. Bun le Bun les Kimberl Air Tours 2014